The field of the invention is jet injection methods and devices.
Various jet injection methods and devices have been known and used in the past. Jet injection devices typically have primarily used compressed gas or springs to rapidly drive a piston or plunger into an ampule having a small diameter nozzle. The high fluid pressure within the ampule, generated by the large force on the plunger, causes a jet or stream of fluid to flow from the nozzle at a pressure and velocity sufficient to penetrate the skin.
Jet injection has several advantages over conventional needle and syringe injections. The patient may be more relaxed as no needle is used. Pain experienced during the injection may also be lessened in certain instances. More importantly, after the injection, there is no risk of an accidental stick or puncture with the used needle, thereby significantly reducing the risk to doctors, nurses and others of transmission of infectious disease. In addition, special handling and disposal requirements for the potentially hazardous used needle are lessened.
One area where jet injection would be very helpful is in the treatment of diabetes. Patients with chronic diabetes generally must inject themselves with insulin several times during the day. This procedure requires a continuous supply and repeated handling of needle/syringe combinations, syringe filling steps, and safe and sterile storage of the needle/syringe in between injections. However, insulin injected with a needle/syringe has a certain well known advantageous time-action profile, i.e., the formulation of the insulin, the characteristics of the injection site, and the way the insulin is delivered by the needle into the injection site, combine to allow the insulin to be absorbed into the patient's blood at the desired rate.
As shown in FIG. 1, using a needle/syringe 1, insulin 2 is delivered through the skin 3 into the adipose tissue 4. The adipose tissue is made up of fat and connective tissue. The injected volume of insulin typically forms a bolus 5 in the adipose tissue. The needle/syringe uses low pressures. Consequently, the injected fluid seeks a path of least resistance, approximately isotropic in the adipose tissue. As a result, the injected fluid forms into a bolus generally having a ragged or irregular generally spherical or globular shape. This shape of insulin volume causes a slow absorption of the insulin into the blood. Moreover, blood circulation in the adipose tissue surrounding the bolus is generally relatively low, further slowing the absorption of insulin into the blood. Consequently, the needle/syringe delivery achieves a desired time-action profile of insulin level in the blood.
The use of jet injection for administration of Insulin dates back to at least as early as 1966. In that era, the standard Insulin was fairly quick acting, so patients received several small injections over the course of a day. It has long been recognized that keeping the Insulin level more nearly constant in the bloodstream of diabetics would improve their long term survival, and mitigate some of the complications that result from deviations in Insulin level from the desired natural level. Thus, longer acting formulations of Insulin were sought, and became available to patients in the 1980's. However, these longer acting Insulins were formulated to get the proper time-action profile with a needle/syringe. When these same formulations were administered with previous jet injectors, results were not satisfactory. Jet injection of these Insulins, have produced much faster absorption of the Insulin than desired.
This disadvantage of jet injection arises because jet injection necessarily uses high pressures to create a high velocity fluid jet. As shown in FIG. 2, after piercing the skin, the jet 6 forms a deposit 7 in the adipose tissue which is elongated and directed toward the muscle fascia 8. The much higher blood circulation in the muscle 9 and the muscle fascia 8 boundary produce much faster absorption of the insulin (or other injectant) into the blood stream. In addition, the high velocity of the injected jet causes mixing of the fluid with the adipose tissue, again promoting a more rapid than desirable absorption into the blood stream. Thus, jet injection, despite its advantages, has not been generally acceptable for diabetics using modern long acting Insulin formulations.